SAN FRANCISCO — The California Supreme Court ruling legalizing gay marriage will not be the last word.

California voters will almost certainly hold a referendum on a constitutional amendment banning same-sex marriage in November, and for the first time anywhere in the U.S., the vote will have a direct and immediate effect on gay couples waiting to tie the knot.

The amendment needs a simple majority to pass, and if the voters reject gay marriage, their decision will supersede the high court’s. There are signs the contest’s outcome will be close.

It will certainly be costly — the two sides say they plan to spend at least $25 million combined on the campaign.

“The people who want to defeat the amendment are going to have to work very hard to be successful — harder than the people who want the amendment to pass,” said Charles Gossett, a California State University-Pomona political scientist who has analyzed a decades worth of poll numbers on the issue. “But I don’t think its impossible.”

Though the state has a history of being on the vanguard of gay rights, California residents have polled slightly against same-sex rights in recent years.

Opponents have had edge in pollsThe most recent polls, conducted in 2006 and 2007, found that 51 percent and 49 percent of survey respondents opposed making gay marriage legal, while 43 percent and 45 percent endorsed the idea.

Those numbers have remained virtually unchanged since former Gov. Gray Davis signed legislation in 2003 giving registered domestic partners the same rights and benefits as married spouses and since same-sex marriage became legal in Massachusetts in 2004, according to Gossett.

Proponents of the November initiative marriage think the court’s 4-3 ruling will hit closer to home and galvanize moderate voters who don’t mind gay couples entering into domestic partnerships, but want marriage reserved for a man and a woman.

“You may find even increased support from 2000,” when an anti-gay marriage referendum passed easily, said Andrew Pugno of the California Marriage Protection Act campaign. “With this court decision, the need for the marriage amendment is brought into clearer focus.”

Mindful of the defeat suffered by gay marriage opponents two years ago in Arizona — the only state where voters have rejected a marriage amendment — the sponsors deliberately decided against trying to simultaneously repeal domestic partner rights, which two-thirds of California voters support.

National support for both sidesThe secretary of state still must verify the initiative, a decision expected next month.

Groups from across the nation already are pledging resources to defeat or support the measure, similar to gay marriage bans enacted in 26 other states. Colorado-based Focus on the Family and the Democratic Congressional Committee both donated funds during the signature-gathering phase.

The California Conference of Catholic Bishops will not take a position on the measure until it qualifies for the ballot, but “it is obviously an issue they will support,” said spokeswoman Carol Hogan. The church’s position could be a key factor with Latino voters, who have been registering in greater numbers, Gossett said. The pope reiterated his opposition to gay unions on Friday.

Gossett also noted that survey respondents often give what they consider to be politically correct answers on social questions such as gay marriage, but record their true beliefs at the ballot box. A month before 61 percent of California voters approved the 2000 marriage ban, only 52 percent of likely voters told pollsters they favored the proposition.

Corey Cook, a political scientist at the University of San Francisco, said other demographic and political changes will be in play during a presidential election that has attracted the interest of younger voters who tend to be much more accepting of gay relationships.

Will high court delay ruling?
“We have a different electorate than we did eight years ago. They’re more inclined to vote against the constitutional amendment,” Cook said.

Perhaps more importantly, Californians this time might have witnessed hundreds of gay marriages by November. Opponents of gay marriage will ask the high court to stay Thursday’s decision, but the court is not obligated to do so.

If gay marriages become a reality this summer, Cook said, voters will be faced with the choice of disappointing their neighbors and relatives. Some think that will only happen in San Francisco but Cook disagreed.

“People who live in Fresno are going to know gay people who are going to be married,” he said.

California's secretary of state is expected to rule by the end of June whether the sponsors of the anti-gay marriage ballot measure gathered enough signatures to put the amendment on the ballot.

Republican Gov. Arnold Schwarzenegger, who has twice vetoed legislation that would have granted marriage to same-sex couples, said in a statement he respected the court's decision and "will not support an amendment to the constitution that would overturn this state Supreme Court ruling."

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